Process of treating cellulose acetate



Patented Oct. 13, .1925.

UNITED STATES PATENT F C -q EDWARD s. FARROW, are, or ROCHESTER, NEW YORK, assronort T0 EASTMAN KODAK COMPANY, OF nocnns'rnn, NEW YORK; A oom'oaa'rron or NEW YORK.

rnoonss or rnm'rme oELLULosE ACETATE.

No Drawing.

To all whom it may concern: I

Be it known that I, EDWARD S.'FARROW, Jr., citizen of the United States of America, residing at Rochester, in the county of Monroe and State of New York, have invented certain new and useful Improvements in Processes of Treating- Cellulose Acetate, of which the following is a full, clear, and exact specification. This invention relates to a process of treating cellulose acetate insuch a way as to change the solubility thereof. One ob]e ct, of the invention is to .provide'a'process 1n which chloroform-soluble cellulose acetate is quickly, reliably and inexpensively hydrolyzed to the desired degree, say to acetone solubility for instance. Another object of the invention is to-provide fa'process' m which the conversion of chloroform-soluble cellulose acetate to acetoneesoluble cellulose acetate can be so carried out that the quality of the finalacetate will be uniform in sue cessive batches; Still another object ofthe invention is to provide a process forobtarning acetone-soluble cellulose acetate from chloroform-soluble cellulose acetate without impairing the former and without lessening the desired qualities, such as flexib1l1ty,of. products like film, into which itenters. Other objects will hereinafter appear.

I have discovered that chloroform-soluble cellulose acetate maybe changedesoes to be solublejin different organic solvents by d1ssolving it in strong phosphoric acid, either] 1 aqueous solution containing from 70 to 85% ortho or pyro, and maintaining the solution at a moderate temperature until the desired result is'obtained. Iprefer to use chloroform-soluble cellulose acetate, which is in a form having a large surface relative to its mass, su ch as powderorthin film.- This enables meto'dissolve every particle of the material quickly, in order to obtain uni'form action. The time of dissolving is greatly lessened. I have found that thesolutionpf cellulose acetate in strong phosphoric ac d, and the partial hydrolysis of the mater al which takes place while the solution is being kept, occur readily,

even when some of the acetic acid and condensing agent from the original acetylating. react on mass are pres- If the'chloroform soluble cellulose acetateis initially in a solid and comparatively coarse form, I prefer to mechanlcally sub- Application med January 20, 1925.- Srial- No. 3,681. I

' divide it, as by cutting, grinding, crushing and the like; or it may be dissolved in chloroform or other suitable solvents and made into thin films or fiber'sby any of the usual processes. It is also convenient to use an initially fibrous form of chloroform-soluble cellulose acetate, such as that for instance disclosed in U. S. patent to Mork, No. 854,374, May 21, 1907.

For the. sake of simplicity and low cost,

in the preferred form of my invention I utifl lize' chloroform-soluble "'celliilose acetate :whieh isdi rectly derived ifromthe original reaction mass in a form having'aflarge surfaceJ-fi This may be readily done in accordance with the methods disclosed in U. S.

Patents No. 1,494,830, Cook, May 20, 1924:,

process of manufacturing cellulose acetate, No. 1,494,816, Seel, May 20, 1924, process of manufacturing cellulose acetate, and N0. 1,516,225,.Webb, Nov. 18, 1924, process of manufacturing cellulose acetate. In all of J these patents the surface of the,reaction mixture is greatly increased relative to its mass and most of the acetic values such as acetic acld, are conducted away in the form of vapor "and-recovered.

Taking byway o'f illustration a powder produced in the Steel process or the Webb process, prefer to dissolve it in conc'en-;

tra ted'orthophosphoric acid. of a strength ranging from 60% up to the strength which. 7

will just remain liquid at room temperature. A syrupy form of ortho phosphoric acid of the pure acid has been found to be especially useful. The powder is merely dissolved in the acid, using agitation or rapid stirring to make. the action uniform, although it dissolves very quickly in the concentrated syrupy acid, even without agitation. The action takes place even when the chloroform-soluble cellulose acetate I in.

ticular-strength of acid employed is used may dissolve therein one-quarter of its own weight of comminuted cellulose acetate; This is a convenient proportion, although considerably more may be usefully dissolved therein.

The completion of the action can be-readlily detected by vtaking a small sample, prelose acetate, the latter then being washed and dried. Thephosphoric acid may'then, if desired, .be recovered by any suitable process. I

The temperature used during the treatment may be varied over a considerablerange, the change in solubility being effected more quickly as higher temperatures are employed. With ortho phosphoric acid in the syrupy form (70 to 85% for example) a useful range is between F. and 80 F. The time during which the conversion can be effected will vary and is best established by a test as hereinabove described.

\Vhile I prefer to employ ortho phosphoric acid, the closely related pyro phosphoric acid is usable, these being the varieties of phosphoric acid which are liquids above their melting points, in contradistinction to meta phosphoric acid which sublimes.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

p 1. The process which comprises dissolving chloroform-soluble cellulose acetate in asolution of phosphoric acid of a type which ,is liquid above its melting point and partially hydrolyzing it while so dissolved. 2. The process which comprises treating -chloroform-soluble cellulose acetate with ortho phosphoric acidof at least strength until acetone-soluble cellulose acetate is produced.

3. The process which comprises dissolving chloroform-soluble cellulose acetate in syrupy 'orthophosphoric acid of 70 to 85% to dissolve it and partially hydrolyze it while it is so dissolved.

5. The process which comprises dissolving chloroform-soluble cellulose acetate containing acetic acid and a condensing agent in a so- .lution of a type of phosphoric acid which is a liquid above its melting point and maintaining thesolution until acetone-soluble cellulose acetate is produced.

6.The1 process which comprises dissolving. powdered chloroform-soluble cellulose acetate in syrupy ortho phosphoiicncid of 70 to 85% strength and maintaining such solution until acetone-soluble cellulose acetate is produced.

7 The process which comprises dissolving chloroform-soluble cellulose acetate in comminuted form in a concentrated solution of a type of phosphoric acid which is liquid above its melting point, the concentration of the acid being at least 60%, maintaining the solution until acetone-soluble cellulose acetate is produced, precipitating the acid from said solution and purifying it.

8. The process which comprises dissolving a reaction mass containing chloroformsoluble cellulose acetate in a form having a large surface relative to its mass and from which at least part of the acetic values have been removed in a solution of ortho phosphoric acid of greater than 60% strength, maintaining the solution until acetone-soluble cellulose acetate is produced, and finally precipitating and washing said cellulose acetate. i

9. The process which comprises dissolw ing chloroform-soluble cellulose acetate in concentrated phosphoric acid of a type which is a liquid above its melting point, the concentration being above 60% and maintaining said solution at a temperature between 50 F. and 80 F. until acetomsoluble cellulose acetate is produced.

10. The process which comprises dissolving in syrupy ortho phosphoric acid of 70 to 85% strength a reaction mixture in powdered form containing chlorofor111-solublc cellulose acetate and from which at least part of the acetic values have been removed, maintaining said solution at a temperature between 50 F. and 80 F. until acetone-soluble cellulose acetate is produced, and finally precipitating and washing said cellulose acetate.

Signed at Rochester, New York, this 8th day of January, 1925.

EDTVARD S. l iiltllOll', JR. 

